Indicating controller



Jan. 25, 1966 A. R. MYERS INDICATING CONTROLLER Filed April 25, 1963INVENTOR. Alva R. Myers mun-Em JOmPZOo rneys or a thermistor. 'otherthree legs of the Wheatstone bridge.

United States Patent 3,231,802 INDICATING CONTROLLER Alva R. Myers,Mountain View, Calif., assignor to Electronic Processes Corporation, San(Iarlos, Calif., a corporation of California Filed Apr. 25, 1963, Ser.No. 275,641 12 Claims. (Cl. 31829) This invention relates to anindicating controller and more particularly to a controller which can beutilized for maintaining a predetermined set point for any parameterwhich can be expressed as a voltage or a current.

In Patent No. 2,971,137, there is disclosed a power control circuit.This power control circuit does not include anticipating means foranticipating when the set point is reached. Although anticipatingcircuits have heretofore been utilized, there is a need for a controllerin which the anticipating means is completely isolated from the controlmeans.

In general, it is an object of the present invention to provide anindicating controller in which the control means is completely isolatedfrom the anticipating means.

Another object of the invention is to provide an indicating controllerof the above character which can be readily and accurately calibrated.

Another object of the invention is to provide an indicating controllerof the above character in which elements in the anticipating means canbe changed without affecting the calibration of the control means.

Another object of the invention is to provide an indicating controllerof the above character in which a low voltage D.C. servo can be drivenfrom an AC bridge.

Another obiect of the invention is to provide a controller of the abovecharacter which is completely isolated from the power source.

Another object of the invention is to provide a controller of the abovecharacter which is compact, light in weight and which can be readilymanufactured.

Another object of the invention is to provide a controller of the abovecharacter in which the set point can be readily adjusted.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment is set forth indetail in conjunction with the accompanying single figure of the drawingwhich is a schematic circuit diagram of the invention as applied totemperature control.

As shown in the schematic circuit diagram in the drawing, my indicatingcontroller consists of a control bridge B1 and an anticipator bridge B2.Both of the bridges are Wheatstone bridges. The control bridge B1consists of a sensing element for measuring a particular parameter, as,for example, temperature. The sensing element R1 can be of any suitabletype such as a resistor The resistors R2, R3 and R4 form the Apush-toset switch S1 has its contacts 1 and 2 connected across one setor pair of opposite terminals 0 and d of the Wheatstone bridge B1 andhas its movable contact 3 connected to ground as shown. The other pairof terminals a and b of the bridge B1 is connected to a suitable voltagesupply as, for example, a 6.3 volt A.C. supply supplied by the secondarywinding 11 of a transformer T2. Three potentiometers P1, P2 and P3 areserially connected across the last named pair of terminals a and b ofthe control bridge B1. Potentiometers P1 and P3 are used as low and highrange calibration potentiometers, respectively, whereas thepotentiometer P2 is utilized as a servo position potentiometer ashereinafter described.

The terminal d of the control B1 is connected to the terminal c of theanticipator bridge B2. The anticipator bridge consists of twotemperature sensitive resistors such as thermistors TH1 and TH2 whichform two legs of the bridge. The other two legs of the bridge arecompleted by resistors R6 and R8. The pair of terminals a and b of theanticipator bridge B2 are supplied with a suitable voltage supply suchas the 6.3 volt A.C. supply from a winding 12 of the transformer T2. Theoutput of the anticipator bridge B2 is connected to a control amplifierA1 by connecting the input of the control amplifier to the terminal a.of the anticipator bridge B2. The output of the control amplifier A1 iscoupled to the base of an NPN transistor Q1 through a coupling capacitorC1. A resistor R9 is connected to the "base of the transistor Q1 andserves to keep the transistor Q1 normally turned off until a signal isreceived from the control amplifier A1. The emitter of transistor Q1 isconnected to ground as shown. The collector of the transistor Q1 isconnected through a current limiting resistor R10 to one side of thewinding of relay RY1. The other side of the winding is connected to oneside of a diode D1. The other side of the diode D1 is connected to asuitable voltage supply as, for example, 20 volts, 60 cycle A.C., ashereinafter described. A capacitor C3 is connected across the winding ofthe relay RY1 to prevent chattering of the contacts of the relay.

As shown in the circuit diagram, the relay RY1 is provided with contacts16. Stationary contact 1 of the relay is connected to one side of a loador controlled circuit 16 which can be of any desired type as, forexample, the resistive load of an oven indicated by the broken line 17.The resistive load 16 is connected to the terminal L2. Terminals L1 andL2 are connected to a suitable power supply as, for example, volts,50/60 cycle A.C. supply indicated. The terminal L1 is connected tomovable contact 2 of the relay RY1. Thus, when the movable contact 2 ismoved into engagement with the stationary contact 1, power is suppliedto the heating element 16. Stationary contacts 5 and 6 of relay RY1 areconnected to ground through suitable indicating means as, for example,incandescent lamps N1 and N2. In addition, stationary contact 5 is alsoconnected to one side of a current limiting resistor R11 and the otherside of the current limiting resistor is connected to a heater H1 whichis the heater for the thermistor TH1 in the anticipator bridge B2;Likewise, stationary contact 6 of the relay is connected to one side ofthe current limiting resistor R12. The other side of the currentlimiting resistor R12 is connected to a heater H2 which is the heaterfor the thermistor TH2 in the anticipator bridge B2. The other ends ofthe heaters H1 and H2 are connected by a potentiometer P4. The tap 18 ofthe potentiometer P4 is connected to ground. The potentiometer P4 isutilized as a reset adjustment and establishes the duty cycle for therelay RY1.

The point 21 connected to the potentiometer P2 of the control bridge B1is connected to the input of a servo amplifier A2. The output of theservo amplifier is connected to the base of an NPN driver transistor Q2through a coupling capacitor C2. The transistor Q2 is biased through theresistor R14 connected to the base of the transistor so that it willonly conduct when a signal is applied to it by the servo amplifier A2.The emitter of the transistor Q2 is connected to ground as shown. Thecollector of the transistor Q2 is connected through a current limitingdriver protecting resistor R13 to the bases of two PNP \powertransistors Q3 and Q4 through isolating diodes D2 and D3. The base ofthe transistor Q3 is connected to the emitter of the transistor Q3through the stablilizing resistor R15 and similarly, the base of thetransistor Q4 is connected to the collector of the transistor Q4 througha stabilizing resistor R16. The collector of the transistor Q3 isconnected to one side of o the current limiting resistor R17. The otherside of the curent limitingresistor R17 is connected to one side of aD.-C. servo motor 23. The other side of the servo motor is connected tothe collector of the transistor Q4. The collectors of the transistors Q3and Q4- are also connected to taps 24a and 24b on opposite ends of awinding 24 provided with a center tap: 26 through diodes D4 and. D toprovide a suitable voltage to the transistors Q3 and Q4. Isolatingdiodes D5 and D7 are connected between the diodes D4 and D5 and theemitters of the associated transistors Q3 and Q4 and serve to isolatethe emitters from the remainder of the circuitry during certain portionsof the cycle of operation.

The primary winding 27 of the transformer T2 is also connected to thetaps 24a and 24b of the winding 24. The transformer T1 is provided witha primary winding 28 which has its terminals L3 and L4 connected to asuitable power supply such as 110 volts, 50/ 60 cycle A.-C. indicated inthe drawing. One end of the winding 24 is connected to the diode D1 toprovide the Volt 60 cycle A.-C. supply indicated. Isolating shields 29are provided on the transformer T1 to isolate the primary from thesecondary; similarly, shields 31 are provided in the transformer T2 toisolate the secondary from the primary. Since both of the transformersT1 and T2 are provided with separate shielding, it can be seen that theoutput voltage supplied to the windings 11 and 12 are doubly isolatedfrom the power supply connected to the terminals L3 and L4 of thetransformer T1.

The servo motor 23 drives an indicator I1 with a pointer 29 as well asthe potentiometer P2 as shown by the broken line in the drawing.

Operation of my indicating controller may now be briefly described asfollows. Let it be assumed that the indicating controller has been setfor a predetermined set point in a manner hereinafter described by theadjustment of potentiometer R3. Also, let it be assumed that it isdesired to bring the control circuit or load up to the set point from apoint which is considerably below the starting point. Thus, when poweris supplied to the load 16, power is also supplied to the heater H1 tocause the thermistor element THZ to rise in resistance value. When thetemperature of the sensing element R1 is considerably below the setpoint there w-il1 be an output from the control bridge to which is addedthe output of the anticipator bridge. The combined outputs of the twobridges are supplied to the control amplifier A1. Normally, when thesensing element R1 is below the set point temperature, the output of thecontrol bridge B1 will have one phase, whereas if the sensing element R1senses a temperature which is above the set point temperature, thecontrol bridge B1 will have an output of opposite phase or, in otherwords, 180 out of phase with the phase when the sensing element issensing a temperature below the set point temperature. The relay RY1will be operated when the combined output 'from the bridges B1 and B2 isof one phase and will not be operated when the combined output is ofopposite phase. The diode D1 is arranged so that it will only supply thepositive half wave of the 60 cycle A.-C. signals which are supplied toit from the transformer T1. The relay RY1 will only be operated when asignal of one phase is supplied to the base of the transistor Q1 tocause current to flow through the transistor to ground to energize thewinding of the relay RY1. Thus, the relay is phase sensitive.

When the relay RY1 is energized, its contacts 1 and 2 are closed as areits contacts 4 and 5 to apply power to the load 16 and also to applyheat to the heater H1. Thus, at the time that the load 16 is beingsupplied with power, heat is being supplied to the heater H1 and thelamp N1 is lit. Heating of the heater will cause the resistance value ofthe thermistor TH2 to rise in value to cause an unbalance in theanticipator bridge B2 to pro vide an output which is out of phase withthe output of the bridge B1. This output is added to the output from thecontrol bridge B1 which causes the relay RY1 to be deenergized beforethe setpoint is reached.

As soon as the relay RY1 is deenergized, the contacts 4 and 6 are closedto supply heat to the heater H2 which heats the thermistor THZ toincrease its resistance value. As this resistance value changes, theoutput of the anticipator bridge B2 is of the same phase as the outputof the control bridge B1 and is added to the output of the controlbridge B1 so that again there is a net signal which is supplied to thebase of the transistor Q1 so that the relay RY1 is again operated orenergized. As soon as the relay RY1 is operated, heat is again suppliedto the load 16 and to the heater H1. As the heater H1 heats up, theresistance value of the thermistor TH1 again changes to provide anoutput from the anticipator bridge out of phase with the output ofcontrol bridge B1 which added to the control bridge output causes therelay RY1 to be deenergized again. As soon as the relay RY1 isdeenergized, the heater H2 is again energized. This procedure continuesuntil the set point is reached and thereafter serves to maintain the setpoint with very minor temperature fluctuations. Thus, it can be seenthat the anticipator bridge B2 helps the indicating controller toanticipate the set point to thereby reduce or eliminate the initialovershoot and to eliminate any substantial temperature fluctuations whencontrolling at the set point.

In summarizing this operation, it can be seen that the output from thecontrol bridge will be much greater than the output from the anticipatorbridge which has a tendency to cancel the output from the controlbridge. However, the closer to null the set point becomes, the lower theoutput from the control bridge until eventually a point is reached wherethe outputs of the control bridge and the anticipator bridge equal eachother, and since they are out of phase, they will cancel to supply azero signal to the control amplifier A1. As soon as this occurs, thetransistor Q1 stops conducting and the relay RY1 is deenergized causingthe relay to return to its normally open position. This causes heatingof the heater H2 to heat the thermistor THZ to change the output phaseof the anticipator bridge so that it adds to the output of the controlbridge and again causes the transistor Q1 to conduct to again energizethe relay RY1. This causes heating of the heater H1 and the thermistorTH1 to again change the output and phase of the anticipator bridge. Thiscycling continues with the period of time between each cycle being lessto thereby line out violent temperature fluctuations as the set point isreached and thereafter to control the temperature so that it is alwaysvery close to the set point.

As the output from the control bridge B1 changes because of the changein the temperature of the sensing element R1, a signal is supplied fromthe point 21 to the servo amplifier A2. The output of the servoamplifier A2 is coupled to the base of the driver transistor Q2 througha coupling capacitor C2. The collector output of the transistor Q2 issupplied through resistor R13 to phase sensitive circuitry consisting ofthe power transistors Q3 and Q4 and the associated diodes D4 and D5 anddiodes D6 and D7. Thus, when the tap 24a of the transformer winding 24connected to the diode D6 is positive in the first half cycle and thebase of the transistor Q2 is also positive during the first half cycle,the transistor Q3 will be turned on to supply its signal of one polarityto the servo motor 23 through the resistor R17. Conversely, if the phaseis reversed, the transistor Q4 is turned on to supply power in anopposite direction to the servo 23 and also through the diode D4. WhenQ3 is turned on, the collector supply for the transistor Q3 is obtainedthrough the diode D5, and conversely, when the transistor Q4 is turnedon, the collector supply is obtained through the diode D4. Thus,depending upon the signal received from point 21, the servo motor 23will be driven in one direc tion or the other which will cause thepotentiometer P2 to be adjusted by the servo until the signal at 21 hasreduced to zero to thus stop operation of the servo motor 23.

The output from the control bridge will be a sine wave of one phase whenthe sensing element R1 increases in value and will be a sine wave of theopposite phase when the resistance value of the sensing element R1decreases. In the circuitry shown, the positive half cycle of each ofthe sine waves is utilized and supplied to the servo amplifier A2. Thus,in other words, in order to operate the servo motor, a positive signalis required. However, it is readily apparent that, if desired, thenegative portions of the sine wave can be utilized instead of thepostiive portions.

In adjusting the set point, the push-to-set switch S1 is operated toconnect contacts 2 and 3 of the switch S1 and to, in effect, groundterminal d of the control bridge.

Then, by varying the control potentiometer R3, the set. point can beraised or lowered because this will cause a' signal to be supplied tothe servo amplifier A2 to cause rotation of the servo motor 23 and theindicator I1 to the'desired position. The potentiometers P1 and P3 arecalibration potentiometers and are used for determining the' range ofthe indicator and, in particular, the lower anduppe'r points,respectively, of the range.

' At the time that the set point is being set, the 20 volts A.-C.supplied to the diode D1 are removed and the anticipator bridge balancecontrol R8 is adjusted to provide a Zero output at terminal a of theanticipator bridge B2. As soon as the set point has been adjusted, thediode D1 is again connected to the power supply and the push-to-setswitch is opened to close contacts 1 and 3.

I The circuitry hereinbefore described has several particularly novelfeatures. One is the use of a separate anticipator bridge which iscompletely isolated from the control bridge. By utilization of theseparate anticipator bridge, the balance of the control bridge isunaffected by the anticipator bridge. This is even true if elements inthe anticipator bridge are changed.

Another substantial advantage of my indicating controller is that it ispossible to drive a D.-C. type servo motor from A.'-C. bridges whilestill utilizing relatively low D.-C. voltages to make possible the useof relatively inexpensive transistors. The transistors Q2, Q3, Q4 andthe associated diodes provide an excellent phase discriminator whichmakes it possible to utilize the D.-C. servo motor. By utilizing atransistor driver, it is possible to eliminate the need for input andoutput transformers.

It is apparent from the foregoing that I have provided a new andimproved indicating controller. Although I have described my indicatingcontroller as being utilized primarily as a temperature controller, itis readily apparent that it can be utilized to control any set pointwhich can be expressed as a voltage or a current. As is well known tothose skilled in the art, there are many transducers available formeasuring various types of parameters such as wind velocity, streamflow, etc., and which will provide a variable voltage or current outputwhich can be readily used in my indicating controller so that theindicating controller can be utilized for maintaining a predeterminedset point.

I claim:

1. In a controller for controlling the reaching of a predetermined setpoint by a parameter and for maintaining the parameter at apredetermined set point by controlling the application of power to acontrol circuit, a first bridge including a sensing element for sensingthe selected parameter, a second bridge connected to the output of thefirst bridge, first A.-C. power supply means connected to said first andsecond bridges, phase sensitive means connected to the combined outputsof said first and second bridge circuits for determining when thecombined output of said first and second bridge circuits is of one phaseor of an opposite phase, second power supply means, and means controlledby the phase sensitive means and connected to said second power supplymeans and to said control circuit for applying power from said secondpower supply means to said control circuit, said second bridge circuitincluding anticipating elements affected by the operation of said meanscontrolled by said phase sen sitive means.

2. A controller as in claim 1 wherein said anticipating elements in saidsecond bridge circuit are temperature sensitive elements together withmeans controlled by the means controlled by the phase sensitive meansfor changing the temperature of said temperature sensitive elements.

3. A controller as in claim 1 wherein said anticipating elements are inthe form of temperature sensitive resistive elements together withheater means associated with each of the resistive elements, and meanscontrolled by the means controlled by the phase sensitive means forcontrolling the application of power to said heating elements.

4. A controller as in claim 1 wherein said first bridge circuit includesa potentiometer, phase sensitive means connected to said potentiometer,third power supply means, a servo motor connected to said potentiometerfor adjusting said potentiometer, and means connected to said last namedphase sensitive means and to said third :power supply means for drivingsaid servo motor in one direction or an opposite direction dependentupon the phase of the output from the first bridge circuit.

5. A controller as in claim 4 wherein said servo motor is a DC. servomotor and wherein said third power supply is an A.-C. power supply.

6. A controller as in claim 4 together with a common A.-C. supply forsaid first, second and third power suspplies, said first power supplyincluding a first transformer means connected to the common A.-C.supply, and a second transformer connected to said first transformer,and isolating means mounted in each of the trans-formers.

7. In a controller for controlling the reaching of a predetermined setpoint by a parameter and for maintaining the parameter at saidpredetermined set point by controlling the application of power to acontrol circuit, a first bridge circuit including first and second pairsof terminals and a sensing element for sensing the value of saidparameter, a second bridge circuit having first and second pairs ofterminals, a first A.-C. power supply, means connecting the A.-C. powersupply to said first pairs of terminals of said first and second bridgecircuits, means for connecting the second pair of terminals of the firstand second bridge circuits in series so that the outputs of the twobridge circuits are summed, said second bridge circuit including atleast two anticipating elements located in at least two legs of thesecond bridge circuit, each of said bridges having an output of onephase when the 'bridge is out of balance in one direction and of theopposite phase when the bridge is out of balance in the oppositedirection, phase sensitive means connected to the combined outputs ofthe first and second bridge circuits, a second power source, meanscontrolled by said phase sensitive means for supplying power from saidthird power source to said control circuit in accordance with thecondition of said phase sensitive means, means for affecting saidanticipator elements, means controlled by said means for controlling theapplication of power from said third source to said control circuit tosaid means for affecting the anticipator elements in accordance with thecondition of the phase sensitive means, and means for indicating thevalue of the parameter being sensed by the sensing element.

8. A controller as in claim 7 wherein said last named means includes apotentiometer connected across said first pair of terminals of saidfirst bridge circuit, phase sensitive means connected to saidpotentiometer, a third power source, a servo motor, and means controlledby said phase sensitive means connecting said third power source to saidservo motor to drive said servo motor in one direction or the otherdependent upon the phase sensed by the last named phase sensitive means.

9. A controller as in claim 8 wherein said phase sensitive means andsaid means for applying power from said third power source to said servomotor includes a pair of transistors having collector elements connectedto opposite sides of said servo motor and wherein said third powersource is an A.-C. power source, and diode means for connecting oppositeends of said power supply to said collectors.

10. In a controller for controlling the reaching of a predetermined setpoint by a parameter and for maintaining the'parameter at saidpredetermined set point by controlling the application of power to acontrol circuit, a bridge circuit, said'bridge circuit having first andsecond pairs of terminals and a sensing element for sensing the value ofsaid parameter, means for supplying an A.-C. voltage to the first pairof terminals of said bridge circuit, phase sensitive means responsive tothe output of said bridge circuit,a secondsource of power, meansresponsive to the phase sensitive means forcausing the application ofpower to said control circuit in accordance with the condition of saidphase sensitive means, said bridge circuit also including apotentiometer connected across said first pair of terminals ofsaid'b'ridge circuit, a servo motor connected to thepotentiometerfor'driving the potentiometer, a third" A' .-C. power supply, phasesensitive means connected to the output of said bridge circuit, andmeans connected to the phase sensitive means and to said third powersupply for driving said servo motor, said phase sensitive meansincluding a pair of transistors having collector elements connected toopposite sides of said servo motor, and diode means connected to saidcollector elements and to opposite sides of said third A.-C. powersupply;

11. In a controller for controlling the reaching of a predetermined setpoint by a parameter and for maintaining the parameter at saidpredetermined set point by controlling the application of power to acontrol circuit, a first bridge circuit including first and second pairsof terminals and a sensing element for sensing the value of saidparameter, a second bridge circuit having first and second pairs ofterminals, and first and second temperature sensitive resistive elementsin at least two legs of said second bridge circuit, means for supplyingan A.-C. voltage to the first pairs of terminals of said first andsecond bridge circuits, phase sensitive means, means for combining theoutputs of the first and second bridges and connecting the same to thephase sensitive means, a second power supply, control means connected tothe phase sensitive means and to the second power supply for controllingthe application of power to said control circuit, first and secondheating elements for heating the temperature sensitive resistanceelements of the second bridge circuit, said control means includingmeans for applying power to said first and second heating elements inaccordance with the condition of said phase sensitive means, said firstbridge circuit including a potentiometer, a servomotor for driving saidpotentiometer, a third power supply, phase sensitive means for sensingthe output of said first bridge circuit, and means controlled by saidlast named phase sensitive means for controlling the application ofpower to said servo motor to control the movement of the servo motor inaccordance with the phase of the output ofthe" 12. A controller as inclaim 11 together with a com-.-

No references cited.

JOHN F. COUCH, Primary Examiner,

1. IN A CONTROLLER FOR CONTROLLING THE REACHING OF A PREDETERMINED SET PONT BY A PARAMETER AND FOR MAINTAINING THE PARAMETER AT A PREDETERMINED SET POINT BY CONTROLLING THE APPLICATION OF POWER TO A CONTROL CIRCUIT, A FIRST BRIDGE INCLUDING A SENSING ELEMENT FOR SENSING THE SELECTED PARAMETER, A SECOND BRIDGE CONNECTED TO THE OUTPUT OF THE FIRST BRIDGE, FIRST A.-C. POWER SUPPLY MEANS CONNECTED TO SAID FIRST AND SECOND BRIDGES, PHASE SENSITIVE MEANS CONNECTED TO THE COMBINED OUTPUTS OF SAID FIRST AND SECOND BRIDGE CIRCUITS FOR DETERMINING WHEN THE COMBINED OUTPUT OF SAID FIRST AND SECOND BRIDGE CIRCUITS IS OF ONE PHASE OR OF AN OPPOSITE PHASE, SECOND POWER SUPPLY MEANS, AND MEANS CONTROLLED BY THE PHASE SENSITIVE MEANS AND CONNECTED TO SAID SECOND POWER SUPPLY MEANS AND TO SAID CONTROL CIRCUIT FOR APPLYING POWER FROM SAID SECOND POWER SUPPLY MEANS TO SAID CONTROL CIRCUIT, SAID SECOND BRIDGE CIRCUIT INCLUDING ANTICIPATING ELEMENTS AFFECTED BY THE OPERATION OF SAID MEANS CONTROLLED BY SAID PHASE SENSITIVE MEANS. 